METHOD AND APPARATUS FOR DRYING A COATED PAPER WEB

Description

[0001] The present invention relates to a method and an apparatus for drying a coated paper web.

[0002] From the US patents 5771602 and 5230165, it has previously been known to turn a coated but still undried paper web or the like in a non-contacting way by blows generated by a turning device before the web is actually dried in a non-contacting way by airborne web-dryers arranged on both sides of the web.

[0003] From the US patent 5230165, it is also per se known to arrange a curved counterpart provided with underpressure nozzles against the turning device on the other side of the paper web. The purpose is to begin the drying of the paper web on both sides of the web already at the curved section of the web. The said underpressure nozzles have a relatively limited drying capacity, as drying air is blown to flow principally in the direction of the web along the nozzle surface, utilizing the Coanda effect. In the arrangements shown, the moist and still warm drying air blown from the underpressure nozzles is allowed to flow from the counterpart directly into the machine room surrounding the apparatus, which adversely increases moisture and heat in the machine room, in addition to the fact that wasting heat as such does not conform to principles of sound energy economy.

[0004] Due to the Coanda effect, a static underpressure zone is formed between the nozzles and the web in the nozzle area in the said counterparts known per se, principally over the entire nozzle area. The aim is to use this underpressure to intensify the pushing effect of the turning device by means of suction in the counterpart area. Suction is used to spread the web outwards in order to stabilize the web on its curved course. However, regarding these arrangements provided with underpressure nozzles, there is a risk that paper web, should it slacken for example due to tension variations, contacts the nozzles of the counterpart whereupon the coating is damaged and/or the web breaks.

[0005] Patent publication US 3,549,070 shows an arrangement for use in web offset printing or also for heavy boards and even to steel plates. The use of sine wave is mentioned as a solution for light paper webs. Patent publication EP 770 731 shows an arrangement in drying a paper web in a straight dryer and by using a turning device prior to that portion. Nozzles in the turning device are situated on one side of the path.

[0006] The object of the present invention is thus to provide a new, improved method and an apparatus in which the drawbacks presented above have been minimized.

[0007] It especially is an object of the present invention to provide a method and an apparatus with which it is possible to achieve an improved runnability or controllability of a paper web or the like.

[0008] It is further an object of the invention to provide a method and an apparatus which make it possible to lead the paper web or the like more safely through a slot formed by the turning device and the counterpart.

[0009] A further object is to provide a method and an apparatus providing a larger drying capacity of the paper web than before, and thus save space in the machine room.

[0010] It is a further object to provide a method and an apparatus with which it is possible to decrease the moisture and thermal load in the machine room and thus simultaneously improve the energy economy of the process.

[0011] The method and apparatus for drying a coated paper web or the like for achieving the said objects are characterized by what is disclosed in the enclosed independent claims.

[0012] The apparatus of the invention

• in which the running direction of the paper web (W) to be dried is turned in a non-contacting way by using blows generated by blow nozzles of the turning device and by pad pressure thus generated; and in which
• the paper web is dried in a non-contacting way with drying devices;

typically comprises a counterpart provided with overpressure nozzles, the counterpart being arranged at the curved turning device area on the opposite side of the paper web.

[0013] Overpressure nozzles refer hereto nozzles the blows of which generate a web pushing power at all distances from the web. In the known arrangements described above, the starting point has been the reverse; in them, underpressure nozzles have been used for generating at a certain distance from the web a power opposite to the pushing power in order to spread the web. With the overpressure nozzles of the invention, it is possible to control the running of the web better and to ensure that the web stays apart from the nozzles.

[0014] In an advantageous arrangement of the invention, the counterpart may be provided with, for example, Float or Push nozzles disclosed in the applicant's US patent 4384666. On the other hand, if desired, the counterpart may also be provided with simple impingement nozzles which include, for example, a perforated plate or one or more slots extending across the web, from which air is blown principally directly against the web.

[0015] The overpressure nozzles of the counterpart are arranged radially against the blow nozzles of the turning device, i.e. so that blows from the counterpart are directed against the paper web and against the blows from the turning device arranged on the first side of the web. Thus the blows, for example from Float overpressure nozzles, generate a local overpressure on both sides of the web between the paper web and the carrier surfaces of the nozzle, i.e. the nozzle surfaces; with this overpressure, the running of the paper web may be stabilized and the runnability and controllability of the web may be improved. Impingement nozzles provide the same result, although the pressure generated by the impingement nozzles generally is slightly lower than the pressure generated by overpressure nozzles of the Float type.

[0016] On the straight run of the paper web arranged after the turning section, i.e. in the drying section, floating nozzles on the opposite sides of the paper web are, however, arranged advantageously interlaced with each other so that the web travels in a sine-wave path between the nozzles arranged on both sides of the web, which allows an as smooth as possible web run.

[0017] In the turning section of the device, the running direction of the web may be turned even 20°-260°, typically 30°-160°.

[0018] The actual turning device of the invention, in which the running direction of the paper web may be turned 20°-260°, comprises typically 3-15 blow nozzles. The counterpart comprises the same number of overpressure nozzles, i.e. 3-15 nozzles. Also the blow nozzles of the actual turning device are overpressure nozzles.

[0019] According to the invention, the pushing nozzles of both the turning device and the counterpart are principally so-called Float overpressure nozzles of the applicant. As the nozzles in the turning section additionally are arranged opposite to each other on both sides of the web, the pushing forces caused by the nozzle flows are directed against each other. This generates a local overpressure at the carrier surface areas of the nozzles on both sides of the web. The local overpressures arranged opposite to each other on both sides of the web have a stabilizing effect on the web run, and improve the runnability and controllability of the web, also in cases of disturbance. Thus the arrangement of the invention provides an optimal configuration of nozzles as to the control of the web.

[0020] With the arrangement of the invention, in which overpressure nozzles, such as Float nozzles, are used in the counterpart instead of underpressure nozzles known per se, such as Foil or Pull nozzles disclosed in the applicant's patent US 4247993, for example the important advantage is achieved compared with the known technology, that it is considerably less probable that, due to tension variations, the paper web would contact the nozzles of the counterpart or the turning device, because the overpressure nozzle pushes the web away, while an underpressure nozzle is not necessarily always able to keep the web away from the nozzle surface.

[0021] The turning device of the invention is further advantageously provided with a control device, increasing the controllability of the turning device and making it possible to automatically control the distance between the turning device and the web, this control being based on the ratio between the supply air pressure of the turning device and the pad pressure. In addition, the pressures may be used for automatically calculating the tension of the web.

[0022] Thereby the control device typically comprises

• a pressure sensor arranged in the blow nozzles of the turning device for measuring the internal pressure P_SP of the blow nozzle;
• a second pressure sensor arranged between the turning device and the paper web for measuring the pad pressure P_KL between the turning device and the paper web; and
• a control element with which the values of the various pressure sensors are combined in order to calculate the distance H between the nozzle surface of the turning device and the paper web and/or in order to adjust it to a desired level.

[0023] For the calculation of web tension,

• a third pressure sensor arranged between the counterpart and the paper web for measuring the pressure P_VK between the counterpart and the paper web

is additionally needed.

[0024] The distance H between the nozzle surface of the turning device and the paper web is, within the typical range of 0-30 mm, derived from the formula:


in which

H

is the distance (mm) between the nozzle surface and the paper web;

P_SP

is the internal pressure (Pa) of the blow nozzles;

P_KL

is the pad pressure (Pa) of the turning device, i.e. the pressure between the turning device and the paper web, measured in the turning device in the free space between the nozzles;

a

is the amplification coefficient for the machine;

b

is the difference variable for the machine.

[0025] The pad pressure refers to overpressure in the turning device, generated into the turning device, as a box or a similar structure arranged around it restricts the discharge of blowing air from the turning device. With a certain turning device structure, the pad pressure is principally dependent on the amount of air led to the turning device, the pressure prevailing in the counterpart, and the tension of the web. The pad pressure is measured in the free space between the nozzles of the turning device.

[0026] The distance between the carrier surface of the nozzles and the paper web is generally controlled either by adjusting the operating speed of the blower blowing air to the blow nozzles of the turning device, or by a guide vane adjuster so that, by controlling the air supply in this way, also the nozzle pressure P_SP of the blow nozzles, and thus also the distance of the web from the nozzles, is controlled.

[0027] The automatic adjustment of the distance between the carrier surface of the turning device nozzles and the paper web is in practice carried out so that the internal pressure P_SP of the nozzle of the turning device and the pad pressure P_KL between the paper web and the turning device are measured automatically by two pressure sensors, whereafter the distance of the web from the nozzle surface is automatically calculated with the help of the ratio between the internal pressure in the nozzle (nozzle pressure) and the pad pressure, using the above mentioned formula. When necessary, this ratio may be corrected by adjusting the supply of blowing air so that the distance of the web from the nozzle surface remains at a desired level. The adjustment may be automatic, in which case the aim is usually to maintain the distance constant by keeping the ratio between the nozzle pressure and pad pressure constant.

[0028] The web run may thus be corrected with the said pressure adjustment, for example, in a case in which the paper web is drawn away from the nozzle surface due to the decrease in web tension. As the web tension decreases, the pad pressure of the turning device decreases and the ratio between the nozzle pressure P_SP and the pad pressure P_KL increases. By reducing the supply of air to the nozzles, for example, by reducing the operating speed of the blower or by adjusting the guide vanes, the nozzle pressure may thus be automatically reduced whereupon the ratio of the nozzle pressure and the pad pressure, and thus also the distance of the web from the nozzle surface, decreases.

[0029] Besides the web distance, also the paper web tension T may automatically be monitored on the basis of values from the pressure sensors, using the following formula


in which

C

is the amplification coefficient relating to the machine in question within the range of 0.7-1.4, typically 1.0;

P_KL

is the pad pressure (Pa) for the turning device, i.e. the pressure between the turning device and the paper web, measured in the turning device in the free space between the nozzles;

P_VK

is the pressure (Pa) in the counterpart, measured in the free space between the nozzles;

k_VK

is a parametre relating to the machine in question within the range of 0.6-1, typically 0.8;

r

is the radius (m) of the turning device;

h

is the distance (m) between the nozzle surface of the turning device and the paper web;

T

is the tension (N/m) of the paper web;

M

is the grammage (kg/m²) of the paper web;

v

is the speed (m/s) of the paper web.

[0030] The calculated tension value may be used for controlling the tension adjustment. A static pressure P_VK deviating from the atmospheric pressure may be generated between the web and the counterpart, which is dependent on the running mode, and on the supply and discharge of air; this pressure may be above or below the atmospheric pressure, in which case it has to be taken into account when calculating the tension. It may be mentioned that the pressures given in this application generally refer to pressures in relation to the atmospheric pressure, unless stated otherwise.

[0031] The pressure in the counterpart also affects the pad pressure between the turning device and the web. By adjusting the pressure in the counterpart, within the range from overpressure to underpressure, the web run may thus also be controlled from the counterpart side.

[0032] When desired, the overpressure nozzles of the counterpart, as well as the blow nozzles of the turning device, may be used for blowing hot air onto the paper web, the temperature of air being 100-450°C, preferably 150-400°C, and the speed of air 20-100 m/s, preferably 40-80 m/s so that the paper web may efficiently be dried from both sides of the web already in the turning section. In the turning section, a more efficient drying is achieved by overpressure nozzles than by underpressure nozzles, due to better nozzle geometry. With the overpressure nozzles, a bigger heat transmission coefficient may be achieved than with underpressure nozzles, due e.g. to the turbulence of the air flow being discharged from them.

[0033] As the web is dried after the turning device by using airborne web-dryer units provided with exhaust air channels, hot blowing air is discharged from the turning device and the counterpart through the said exhaust air channels of the airborne web-dryer units. Thus moist and hot air is not led from the turning section to the machine room to increase its moisture and thermal load.

[0034] The turning device on the first side of the paper web and the airborne web-dryer unit following it may advantageously be covered with a common housing structure. Likewise, the counterpart on the opposite side of the web and the airborne web-dryer unit following it may advantageously be covered with a common housing structure.

[0035] As a summary it may be said that the following advantages are achieved with the two-sided turning device of the invention, i.e. a turning device provided with a counterpart of the invention:

• good runnability and controllability of the web, also automatically;
• reliable follow-up of the web tension;
• non-contacting travel of the web;
• higher web speed possible;
• more efficient drying possible;
• better energy economy, due to the reduction of moisture and thermal load in the machine room, as the free draws decrease and the recovery of exhaust air becomes possible, and due to the recycling of exhaust air from the airborne web-dryer to the turning device;
• saving of space, due to the better vaporization efficiency in the longitudinal direction of the web, because it is possible to maintain the performance characteristics typical of the airborne web-dryer in the counterpart, e.g. blowing speed 40-80 m/s, temperature 200-400°C, and vaporization 60-180 kg/m²h.

[0036] The invention is next described in more detail referring to the enclosed drawings in which

Fig. 1

is a schematic, partially vertical section of a two-sided turning device of the invention;

Fig. 2

is a schematic view of a control system of the two-sided turning device of Fig. 1; and

Fig. 3

is a schematic, enlarged view of an overpressure nozzle used in the counterpart of the invention.

[0037] Fig. 1 shows a two-sided turning device 10 in accordance with the invention for drying a coated paper web W. The device comprises a device 12 turning the running direction of the paper web, and a drying apparatus 14 arranged in the running direction of the web after the web turning device.

[0038] The turning device comprises the actual turning device 16 on the first side of the web, in the case shown in the Figure above the web, and a counterpart 18 for this device on the second side of the web. The turning device 16 comprises six blow nozzles 20 which, in the case of the Figure, are overpressure nozzles of the so-called Float type of the applicant. The Float nozzles are symmetrical nozzles, from the longitudinal slots on both edges transverse to the web of the carrier surface of which blows are directed against each other and against the web, forming an overpressure zone between the nozzle and the web, and turning the running direction of the web about 70-80 degrees, in the case shown in the Figure. The turning device 16 of the Figure has its own air system with air supply channels 22 for bringing make-up air to the turning device. In the turning device, air in the machine room, exhaust air from the airborne web-dryer, circulating air, or a mixture of these, for example, may be used as blowing air.

[0039] The counterpart 18 has likewise six overpressure nozzles 24 arranged on the second side of the web exactly opposite to the nozzles 20 of the turning device. The counterpart may have an air supply system of its own with air supply channels 26, as is shown in broken lines in Fig. 1. The counterpart may also have its own exhaust or return air system with exhaust air channels 28, into which air blown against the web is absorbed, as is also shown in broken lines in Fig. 1. However, the supply and discharge of air in the counterpart may advantageously be arranged through the drying apparatus, as is explained below.

[0040] The drying apparatus 14 is an airborne web-dryer with separate airborne web-dryers or airborne web-dryer units 30 and 30' on both sides of the web. The upper airborne web-dryer unit 30 is combined with the turning device 16 under the same housing structure 32. However, the turning device is separated from the airborne web-dryer unit by a partition 39. The said airborne web-dryer unit 30 above the web has its own air supply system with air supply channels 34. The airborne web-dryer unit 30 also has its own exhaust air system with exhaust air channels 36. From the turning device 16, air is transferred along with the web to the upper airborne web-dryer unit, as is in an exemplary way shown with arrow 38, and from there onwards into the exhaust air channel 36. The necessary amount of make-up air is brought to the turning device.

[0041] The lower airborne web-dryer unit 30' is connected in a similar way to the counterpart 18 with a common housing structure 40. Exhaust air from the counterpart is arranged to flow into the exhaust air channel 36' of the airborne web-dryer unit 30'. Supply air, i.e. pressurized blowing air is led to the counterpart through the air supply channel 34' of the airborne web-dryer unit 30'. The supply air systems for the airborne web-dryer 30' and the counterpart 18, as well as the exhaust air systems, may be separated from each other by a partition 42 restricting the flow, which is provided with an adjustable damper 44 or a similar element, as is shown in broken lines in Fig. 1, with which the supply of air of the counterpart may be adjusted separately from the air flows of the airborne web-dryer unit.

[0042] In the airborne web-dryer units 30, 30', the floating or blow nozzles 46 and 46' are interlaced so that the web runs in a sine-wave form through the straight airborne web-dryer section.

[0043] Fig. 1 also indicates the pressure measurements for the control system of the turning device. The pressure sensor 48 arranged into the blow nozzle 20 of the actual turning device 16 measures the nozzle pressure P_SP of the nozzle. The pressure sensor 50 arranged between the nozzles 20 of the turning device measures the pad pressure P_KL of the turning device.

[0044] The pressure sensor 56 arranged between the nozzles 24 of the counterpart may respectively be used for measuring the possible underpressure or overpressure P_VK in the counterpart.

[0045] In Fig. 1, the small arrows indicate how the blows from the nozzles 20 and 24 arranged on both sides of the web blow against each other, forming a local overpressure between the nozzle carrier surfaces 52 and 54 and the paper web on both sides of the web. These local overpressures have a stabilizing effect on the paper web and improve the runnability and controllability of the web.

[0046] Fig. 3 shows an enlargement of an overpressure nozzle 24 of the US patent 4,384,666 used in a counterpart of the invention. The arrows indicate the direction of the blows from the carrier surface 54 towards the web.

[0047] The control system for a two-sided turning device in accordance with the invention is shown in more detail in Fig. 2. It may be seen from Fig. 2, that the measuring results from the differential pressure instruments 48 and 50 are led to the control device 58 with which it is possible to control the blower 60 feeding air into the air supply channel 22 of the turning device 16.

[0048] Also the air supply channels 34 and 34' and exhaust air channels 36 and 36' in the airborne web-dryer units 30 and 30' may be seen in the Figure. Fig. 2 shows the alternative in which both the supply air and the exhaust air arrangement of the counterpart are connected to the airborne web-dryer unit 30'.

[0049] The invention is above described in an exemplary way, referring mainly to one embodiment. The purpose is by no means to restrict the invention to this embodiment only, but the invention is intended to be widely applied within the scope of protection defined by the enclosed claims.

Claims

1. Method for drying a coated paper web (W) in a device (10) comprising sequentially in the running direction of the web

- a web turning device (16) arranged on a first side of the web and provided with overpressure blow nozzles (20) directing a pushing force against the web;

- web drying devices (30, 30') arranged on the first and the second sides of the web, the drying devices of the web comprising airborne web-dryer units (30, 30') provided with exhaust air channels (36, 36') and arranged on both sides of the web,

and in which method

- the running direction of the web (W) to be dried is turned in a non-contacting way by blows generated by said blow nozzles (20) in the turning device (16);

- the web is thereafter dried in a non-contacting way by said drying devices; and

- the web run is further stabilized by blows which are generated in the turning device area by overpressure nozzles (24) of a counterpart (18) arranged on the second side of the web, the overpressure nozzles directing a pushing force against the web pushing the web, wherein air blown from the overpressure blow nozzles (20) of the turning device and/or air blown from the overpressure nozzles (24) of the counterpart is absorbed into the exhaust air channels of the airborne web-dryer units, and the blows from the overpressure nozzles (24) of the counterpart (18) are directed towards the second side of the web against the overpressure blow nozzles (20) of the turning device arranged on the first side, the overpressure nozzles (24) of the counterpart (18) and the overpressure blow nozzles of the turning device being opposite to each other on both sides of the web.

2. Method according to claim 1, characterized in that the overpressure nozzles (24) of the counterpart (18) are used for blowing hot air, the temperature of which is 100-450°C, preferably 150-400°C, and the speed 20-100 m/s, preferably 40-80 m/s.

3. Method according to claim 1, characterized in that air is discharged from the turning device mainly into the airborne web-dryer unit (30) arranged after the turning device.

4. Method according to claim 1, characterized in that the web run is additionally controlled by adjusting the pressure prevailing in the counterpart, in the free space between the nozzles.

5. Apparatus (10) for drying a coated paper web (W), comprising sequentially in the running direction of the web

- a turning device (16) arranged on a first side of the web and provided with overpressure blow nozzles for turning the running direction of the web (W) to be dried in a non-contacting way by using overpressure blows generated by said blow nozzles (20), and directing a pushing force against the web; and

- drying apparatuses (30, 30') arranged on the first and the second sides of the web and provided with floating nozzles (46, 46') for non-contacting drying of the web; the apparatus further comprising a counterpart (18) provided with overpressure nozzles (24) and arranged on the second side of the web in the turning device area, the counterpart being provided with said overpressure nozzles (24) for generating overpressure blows which generate a force pushing the web away, wherein the drying apparatuses (30, 30') are airborne web-dryer units arranged on the first and the second sides of the web, and provided with exhaust air channels (36, 36') for discharging blowing air from the space between the floating nozzles (46, 46') and the web, and the overpressure blow nozzles (20) of the turning device (16) and the overpressure nozzles (24) of the counterpart (18) are symmetrical overpressure nozzles and are arranged opposite to each other on both sides of the web, thus forming an overpressure zone between the nozzles and the web on both sides of the web.

6. Apparatus according to claim 5, characterized in that

- the space between the turning device (16) and the web (W) is connected to the exhaust air channel (36) of the airborne web-dryer unit (30) on the first side of the web for discharging air blown from the turning device; and/or

- the space between the counterpart (18) and the web (W) is connected to the exhaust air channel (36') of the airborne web-dryer unit (30') on the second side of the web for discharging air blown towards the web by the overpressure nozzles (24) of the counterpart.

7. Apparatus according to claim 5, characterized in that the apparatus comprises a housing structure (40) covering the part of the counterpart (18) facing away from to web, the housing structure comprising an exhaust air channel (28) for absorbing the air blown towards the paper web from the space between the web and the overpressure nozzles (24) of the counterpart.

8. Apparatus according to claim 5, characterized in that the apparatus has a common housing structure (40) covering the drying apparatus (30') arranged on the second side of the web and the counterpart (18) arranged on the same side, the housing structure including an exhaust air channel (36') for absorbing drying air and air blown through the overpressure nozzles in the counterpart.

9. Apparatus according to claim 5, characterized in that

- the turning device (16) comprises 3-15 overpressure blow nozzles (20) arranged over the web on the first side of the web; and that

- the counterpart (18) comprises 3-15 overpressure nozzles (24) arranged over the web on the second side of the web, the overpressure nozzles of the counterpart (18) being arranged to blow towards the web to a point in which an overpressure blow nozzle (20) of the turning device (16) is found on the first side of the web.

10. Apparatus according to claim 5, characterized in that

- the apparatus comprises a housing structure (32), covering the turning device and the airborne web-dryer (30) arranged adjacent to the turning device; and that

- a partition is provided between the turning device and the airborne web-dryer for maintaining pad pressure in the turning device.

Ansprüche

1. Verfahren zum Trocknen einer beschichteten Papierbahn (W) in einer Vorrichtung (10), die in einer Aufeinanderfolge in der Laufrichtung der Bahn aufweist:

- eine Bahnwendevorrichtung (16), die an einer ersten Seite der Bahn angeordnet ist und mit Überdruckgebläsedüsen (20) versehen ist, die eine Drückkraft gegen die Bahn richten;

- Bahntrockenvorrichtungen (30, 30'), die an der ersten und der zweiten Seite der Bahn angeordnet sind, wobei die Trockenvorrichtungen der Bahn Lufttrage-Bahntrocknereinheiten (30, 30') aufweisen, die mit Abluftkanälen (36, 36') versehen sind und an beiden Seiten der Bahn angeordnet sind; und

in diesem Verfahren

- die Laufrichtung der zu trocknenden Bahn (W) in einer kontaktfreien Weise mittels Blasströmungen gewendet wird, die mittels Gebläsedüsen (20) in der Wendevorrichtung (16) erzeugt werden;

- die Bahn danach in einer kontaktfreien Weise durch die Trockenvorrichtungen getrocknet wird; und

- der Bahnverlauf weiter stabilisiert wird durch Blasströmungen, die in dem Wendevorrichtungsbereich durch Überdruckdüsen (24) eines Gegenstücks (18) erzeugt werden, das an der zweiten Seite der Bahn angeordnet ist, wobei die Überdruckdüsen eine Drückkraft gegen die Bahn richten, die die Bahn drückt, wobei geblasene Luft von den Überdruckgebläsedüsen (20) der Wendevorrichtung und /oder geblasene Luft von den Überdruckdüsen (24) des Gegenstücks in die Abluftkanäle der Lufttrage-Bahntrocknereinheiten absorbiert wird, und die Blasströmungen von den Überdruckdüsen (24) des Gegenstücks (18) in Richtung zu der zweiten Seite der Bahn gegen die Überdruckgebläsedüsen (20) der Wendevorrichtung, die an der ersten Seite angeordnet ist, gerichtet werden, wobei die Überdruckdüsen (24) des Gegenstücks (18) und die Überdruckgebläsedüsen der Wendevorrichtung zueinander entgegengesetzt an beiden Seiten der Bahn angeordnet sind.

2. Verfahren nach Anspruch 1,
dadurch gekennzeichnet, daß
die Überdruckdüsen (24) des Gegenstücks (18) zum Blasen von Heißluft verwendet werden, wobei deren Temperatur 100 bis 450°C, vorzugsweise 150 bis 400°C beträgt, und die Geschwindigkeit 20 bis 100 m/s beträgt, vorzugsweise 40 bis 80 m/s.

3. Verfahren nach Anspruch 1,
dadurch gekennzeichnet, daß
Luft von der Wendevorrichtung hauptsächlich in die Lufttragebahntrocknereinheit (30) ausgestoßen wird, die nach der Wendevorrichtung angeordnet ist.

4. Verfahren nach Anspruch 1,
dadurch gekennzeichnet, daß
der Bahnverlauf zusätzlich gesteuert wird durch ein Einstellen des in dem Gegenstück vorherrschenden Drucks in den freien Raum zwischen den Düsen.

5. Vorrichtung (10) zum Trocknen einer beschichteten Papierbahn (W), die in Aufeinanderfolge in der Laufrichtung der Bahn aufweist:

- eine Wendevorrichtung (16), die an einer ersten Seite der Bahn angeordnet ist und mit Überdruckgebläsedüsen versehen ist zum Wenden der Laufrichtung der zu trocknenden Bahn (W) in einer kontaktfreien Weise unter Anwendung von durch die Gebläsedüsen (20) erzeugten Überdruckblasströmungen, und zum Richten der Drückkraft gegen die Bahn; und

- Trockenvorrichtungen (30, 30'), die an der ersten und der zweiten Seite der Bahn angeordnet sind und mit Flotationsdüsen (46, 46') für ein kontaktfreies Trocknen der Bahn versehen sind;

wobei die Vorrichtung des weiteren aufweist:

- ein Gegenstück (18), das mit Überdruckdüsen (24) versehen ist und an der zweiten Seite der Bahn in dem Bereich der Wendevorrichtung angeordnet ist, wobei das Gegenstück mit den Überdruckdüsen (24) versehen ist zum Erzeugen von Überdruckblasströmungen, die eine die Bahn wegdrückende Kraft erzeugen, wobei die Trockenvorrichtungen (30, 30') Lufttrage-Bahntrocknereinheiten sind, die an der ersten und zweiten Seite der Bahn angeordnet sind, und mit Abluftkanälen (36, 36') versehen sind zum Ausstoßen vom Gebläseluft aus dem Raum zwischen den Flotationsdüsen (46, 46') und der Bahn, und die Überdruckgebläsedüsen (20) der Wendevorrichtung (16) und die Überdruckdüsen (24) des Gegenstücks (18) symmetrische Überdruckdüsen sind, und zueinander entgegengesetzt an beiden Seiten der Bahn angeordnet sind, womit sie eine Überdruckzone zwischen den Düsen und der Bahn an beiden Seiten der Bahn ausbilden.

6. Vorrichtung nach Anspruch 5,
dadurch gekennzeichnet, daß

- der Raum zwischen der Wendevorrichtung (16) und der Bahn (W) mit dem Abluftkanal (36) der Lufttragebahntrocknereinheit (30) an der ersten Seite der Bahn verbunden ist, um von der Wendevorrichtung geblasene Luft auszustoßen; und / oder

- der Raum zwischen dem Gegenstück (18) und der Bahn (W) mit dem Abluftkanal (36') der Lufttragebahntrocknereinheit (30') an der zweiten Seite der Bahn verbunden ist zum Ausstoßen von Luft, die durch die Überdruckdüsen (24) von dem Gegenstück in Richtung auf die Bahn geblasen wird.

7. Vorrichtung nach Anspruch 5,
dadurch gekennzeichnet, daß
die Vorrichtung eine Gehäusestruktur (40) aufweist, die den Teil des Gegenstücks (18) abdeckt, der von der Bahn weggewandt ist, wobei die Gehäusestruktur einen Abluftkanal (28) zum Absorbieren der Luft aufweist, die in Richtung auf die Papierbahn hin aus dem Raum zwischen der Bahn und den Überdruckdüsen (24) des Gegenstücks geblasen wird.

8. Vorrichtung nach Anspruch 5,
dadurch gekennzeichnet, daß
die Vorrichtung eine gemeinsame Gehäusestruktur (40) hat, die die Trockenvorrichtung (30'), die an der zweiten Seite der Bahn angeordnet ist, und das Gegenstück (18) abdeckt, das an derselben Seite angeordnet ist, wobei die Gehäusestruktur einen Abluftkanal (36') zum Absorbieren von Trockenluft und Luft einschließt, die durch die Überdruckdüsen in dem Gegenstück geblasen wird.

9. Vorrichtung nach Anspruch 5,
dadurch gekennzeichnet, daß

- die Wendevorrichtung (16) 3 bis 15 Überdruckgebläsedüsen (20) aufweist, die über der Bahn an der ersten Seite der Bahn angeordnet sind; und daß

- das Gegenstück (18) 3 bis 15 Überdruckdüsen (24) aufweist, die über der Bahn an der zweiten Seite der Bahn angeordnet sind, wobei die Überdruckdüsen des Gegenstücks (18) so angeordnet sind, dass sie in Richtung auf die Bahn zu einem Punkt blasen, an dem sich eine Überdruckgebläsedüse (20) der Wendevorrichtung an der ersten Seite der Bahn befindet.

10. Vorrichtung nach Anspruch 5,
dadurch gekennzeichnet, daß

- die Vorrichtung eine Gehäusestruktur (32) aufweist, die die Wendevorrichtung und den Lufttragebahntrockner (30) abdeckt, der benachbart zu der Wendevorrichtung angeordnet ist; und daß

- eine Abtrennung zwischen der Wendevorrichtung und dem Lufttragebahntrockner vorgesehen ist zum Aufrechterhalten eines Polsterdrucks in der Wendevorrichtung.

Revendications

1. Procédé destiné à sécher une bande de papier couché (W) dans un dispositif (10) comportant de manière séquentielle dans la direction de défilement de la bande :

- un dispositif de renvoi de bande (16) disposé sur un premier côté de la bande et pourvu de buses de soufflage à surpression (20) qui dirigent une force de poussée contre la bande;

- des dispositifs de séchage de bande (30, 30') disposés sur les premier et deuxième côtés de la bande, les dispositifs de séchage de la bande comportant des unités de séchoir de bande en suspension (30, 30') pourvues de canaux d'air d'échappement (36, 36') et disposées des deux côtés de la bande;

dans lequel procédé :

- la direction de déplacement de la bande (W) devant être séchée est tournée d'une manière sans contact par des souffles générés par lesdites buses de soufflage (20) dans le dispositif de renvoi (16);

- la bande est ensuite séchée d'une manière sans contact par lesdits dispositifs de séchage; et

- le cours de la bande est en outre stabilisé par des souffles qui sont générés dans la zone de dispositif de renvoi par des buses à surpression (24) d'une contrepartie (18) disposée sur le deuxième côté de la bande, les buses à surpression dirigeant une force de poussée contre la bande qui pousse la bande, l'air soufflé depuis les buses de soufflage à surpression (20) du dispositif de renvoi et/ou l'air soufflé depuis les buses à surpression (24) de la contrepartie étant absorbé dans les canaux d'air d'échappement des unités de séchoir de bande en suspension, et les souffles provenant des buses à surpression (24) de la contrepartie (18) étant dirigés vers le deuxième côté de la bande à l'encontre des buses de soufflage à surpression (20) du dispositif de renvoi disposé sur le premier côté, les buses à surpression (24) de la contrepartie (18) et les buses de soufflage à surpression du dispositif de renvoi étant disposées à l'opposée l'une de l'autre des deux côtés de la bande.

2. Procédé selon la revendication 1, caractérisé en ce que les buses à surpression (24) de la contrepartie (18) sont utilisées afin de souffler de l'air chaud, dont la température est de 100 à 450°C, de préférence de 150 à 400°C, et la vitesse de 20 à 100 m/s, de préférence 40 à 80 m/s.

3. Procédé selon la revendication 1, caractérisé en ce que l'air est refoulé depuis le dispositif de renvoi principalement dans l'unité de séchoir de bande en suspension (30) disposée après le dispositif de renvoi.

4. Procédé selon la revendication 1, caractérisé en ce que le cours de la bande est commandé en plus en ajustant la pression qui règne dans la contrepartie, dans l'espace libre entre les buses.

5. Appareil (10) destiné à sécher une bande de papier couché (W), comportant d'une manière séquentielle dans la direction de déplacement de la bande :

- un dispositif de renvoi (16) disposé sur un premier côté de la bande et pourvu de buses de soufflage à surpression destinées à tourner la direction de défilement de la bande (W) devant être séchée d'une manière sans contact en utilisant des souffles à surpression générés par lesdites buses de soufflage (20), et à diriger une force de poussée contre la bande; et

- des appareils de séchage (30, 30') disposés sur les premier et deuxième côtés de la bande, et pourvus de buses flottantes (46, 46') pour un séchage sans contact de la bande;
l'appareil comportant en outre une contrepartie (18) pourvue de buses à surpression (24) et disposée sur le deuxième côté de la bande dans la zone de dispositif de renvoi, la contrepartie étant pourvue desdites buses à surpression (24) destinées à générer des souffles à surpression qui génèrent une force repoussant la bande, les appareils de séchage (30, 30') étant des unités de séchoir de bande en suspension disposées sur les premier et deuxième côtés de la bande, et pourvues de canaux d'air d'échappement (36, 36') destinés à refouler de l'air de soufflage depuis l'espace entre les buses flottantes (46, 46') et la bande, et les buses de soufflage à surpression (20) du dispositif de renvoi (16) et les buses à surpression (24) de la contrepartie (18) étant des buses à surpression symétriques et étant disposées à l'opposé l'une de l'autre sur les deux côtés de la bande, en formant ainsi une zone de surpression entre les buses et la bande sur les deux côtés de la bande.

6. Appareil selon la revendication 5, caractérisé en ce que :

- l'espace entre le dispositif de renvoi (16) et la bande (W) est relié au canal d'air d'échappement (36) de l'unité de séchoir de bande en suspension (30) sur le premier côté de la bande, afin de refouler de l'air soufflé depuis le dispositif de renvoi; et/ou

- l'espace entre la contrepartie (18) et la bande (W) est relié au canal d'air d'échappement (36') de l'unité de séchoir de bande en suspension (30) sur le deuxième côté de la bande afin de refouler de l'air soufflé vers la bande par les buses à surpression (24) de la contrepartie.

7. Appareil selon la revendication 5, caractérisé en ce que l'appareil comporte une structure de logement (40) qui recouvre la partie de la contrepartie (18) orientée à l'écart de la bande, la structure de logement comportant un canal d'air d'échappement (28) destiné à adsorber l'air soufflé vers la bande de papier depuis l'espace entre la bande et les buses à surpression (24) de la contrepartie.

8. Appareil selon la revendication 5, caractérisé en ce que l'appareil a une structure de logement commune (40) qui recouvre l'appareil de séchage (30') disposé sur le deuxième côté de la bande et la contrepartie (18) disposée sur le même côté, la structure de logement comprenant un canal d'air d'échappement (36') destiné à absorber de l'air de séchage et de l'air soufflé à travers les buses à surpression dans la contrepartie.

9. Appareil selon la revendication 5, caractérisé en ce que :

- le dispositif de renvoi (16) comporte 3 à 15 buses de soufflage à surpression (20) disposées sur la bande sur le premier côté de la bande; et en ce que

- la contrepartie (18) comporte 3 à 15 buses à surpression (24) disposées sur la bande sur le deuxième côté de la bande, les buses à surpression de la contrepartie (18) étant prévues pour souffler vers la bande vers un point

dans lequel une buse de soufflage à surpression (20) du dispositif de renvoi (16) se trouve sur le premier côté de la bande.

10. Appareil selon la revendication 5, caractérisé en ce que :

- l'appareil comporte une structure de logement (32), qui recouvre le dispositif de renvoi et le séchoir de bande en suspension (30) disposé de façon adjacente au dispositif de renvoi; et en ce que

- une séparation est prévue entre le dispositif de renvoi et le séchoir de bande en suspension afin de maintenir une pression de bloc dans le dispositif de renvoi.

Drawing